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US7840356B2 - Method for determining receiver orientations - Google Patents

Method for determining receiver orientations Download PDF

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Publication number
US7840356B2
US7840356B2 US11/922,814 US92281406A US7840356B2 US 7840356 B2 US7840356 B2 US 7840356B2 US 92281406 A US92281406 A US 92281406A US 7840356 B2 US7840356 B2 US 7840356B2
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receiver
data
model
electromagnetic
inversion
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Expired - Fee Related, expires
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US11/922,814
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US20090171587A1 (en
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Xinyou Lu
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ExxonMobil Upstream Research Co
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ExxonMobil Upstream Research Co
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/12—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with electromagnetic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/083—Controlled source electromagnetic [CSEM] surveying
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/30—Assessment of water resources

Definitions

  • This invention relates generally to the field of geophysical prospecting including reservoir delineation and, more particularly, to controlled-source electromagnetic surveying for geophysical applications. Specifically, the invention is a method for determining electromagnetic receiver orientations.
  • the marine controlled-source electromagnetic (“CSEM”) exploration method uses man-made sources to generate electromagnetic (EM) waves and deploys receivers on the seafloor to record electromagnetic signals.
  • the recorded electromagnetic signals are analyzed to infer subsea floor structures and/or determine nature of particular structures such as reservoirs.
  • FIG. 1 illustrates a typical deployment of CSEM equipment, with an horizontal electric dipole (HED) source 11 towed by a vessel above the water bottom 12 on which receivers 13 are placed.
  • HED horizontal electric dipole
  • receivers fall freely to the seafloor and therefore their orientations are unknown.
  • Receiver orientations are required to determine the three-dimensional EM field vectors measured at receiver locations.
  • the measured fields are then decomposed into components in preferred directions (for example, inline, crossline, and vertical) for analysis, inversion and interpretation. Effects on the decomposed components could be significant when the receiver cannot be oriented to those preferred directions because of inaccurate receiver orientations. Therefore the determination of receiver orientations could significantly affect data interpretation.
  • the present invention provides a technique to determine receiver orientations.
  • receivers In order to completely measure three-dimensional EM fields, receivers need be equipped with three mutually-perpendicular antennas for electric fields and three mutually-perpendicular magnetic sensors for magnetic fields. Three angles are necessary and sufficient to uniquely define the receiver orientations. These three angles establish the relationships between the measurement coordinates and receiver coordinates.
  • a number of ways can be used to define the receiver orientations in the measurement coordinates. They are equivalent and can be converted one another.
  • One way to define the receiver orientations is using azimuth and tilts for two horizontal channels ( FIG. 2 ). In FIG. 2 , (X, Y, Z) are assumed to be the measurement coordinates with X directed to the geodetic east, Y to the geodetic north, and Z upward.
  • (X′′′, Y′′′, Z′′′) are the receiver coordinates and the designed “east”, “north” and vertical channels.
  • (X′, Y′, Z′) and (X′′, Y′′, Z′′) are auxiliary coordinates to help transform coordinates between (X, Y, Z) and (X′′′, Y′′′, Z′′′).
  • X′ is the projection of X′′′ on the horizontal plane XY
  • Y′′ is the projection of Y′′′.
  • the receiver azimuth ( ⁇ ) is defined the angle between Y and Y′
  • the east channel tilt ( ⁇ ) is the angle between X′ and X′′′
  • the north channel tilt ( ⁇ ) is the angle between Y′′ and Y′′′.
  • Polarization analysis was the primary method used in early marine CSEM work to determine receiver azimuth in the subsequent data processing. The method requires at least one towline towed directly over each receiver. Receiver azimuth accuracy provided by this method is not very high. The average error in receiver azimuths is larger than 5 degrees for field data from a boat with a dynamic position system. It could be worse for a ship without a dynamic positioning system in rough weather conditions.
  • Behrens also proposed to use coherency and correlation in natural EM signals recorded by different receivers to determine relative azimuth.
  • This method was developed for receivers without a directly over-towing towline to complement the polarization analysis. The method determines the relative azimuth angle between two receivers. In order to find the receiver azimuth, the method requires the azimuth of the reference receiver be known. Success in using this method is dependent on whether high quality natural signals are recorded by both receivers. Accuracy by this method is normally lower than by polarization analysis.
  • Data interpretation is mainly focused on (and data measurement may be limited to) the inline (meaning along the tow direction) electric component, which is normally not affected much by the tilts if the seafloor is not very steep.
  • the vertical electric component is either not measured or is not fully utilized in data interpretation.
  • No reliable and accurate method is available to determine the receiver orientations. The two tilts are normally small ( ⁇ 10 degrees because the seafloor is normally flat. The three reasons are obviously not completely independent of each other.
  • misalignment ( ⁇ ) with the towline is 15 degrees
  • the inline antenna tilt ( ⁇ ) is up 5 degrees
  • the crossline tilt ( ⁇ ) is down 3 degrees.
  • the modeling frequency is 0.25 Hz.
  • the solid line represents an aligned and level receiver
  • the broken line a misaligned and tilted receiver.
  • the invention is a computer-implemented method for determining three independent angles specifying orientation of electromagnetic receivers in a marine electromagnetic survey, comprising: (a) selecting survey data according to criteria including signal-to-noise ratio and degree of distortion; (b) creating a model representing the survey's source-receiver geometry and media for transmission of electric signal, said model comprising three receiver orientation angles, a resistivity model, and electromagnetic source (transmitter) parameters; and (c) solving Maxwell's electromagnetic field equations with the model and selected survey data as input information and said three orientation angles as unknowns, said solution being performed by iterative numerical inversion.
  • the invention is preferably practiced in the frequency domain in which case the survey data are transformed into the frequency domain by Fourier transform (or other method) before the selecting step above, or at least before the solving/inversion step.
  • FIG. 1 illustrates a marine CSEM survey
  • FIG. 2 defines a set of three angles relating orientation of one coordinate system to another
  • FIG. 3 shows effects of receiver orientations on the amplitude of the inline electric field component
  • FIG. 4 shows effects of receiver orientations on the amplitude of the crossline electric field component
  • FIG. 5 shows effects of receiver orientations on the amplitude of the vertical electric field component
  • FIG. 6 is a flowchart of basic steps in one embodiment of the present inventive method.
  • This invention is a method for determining the orientation of an electromagnetic receiver in a marine CSEM survey by inversion of the electromagnetic field equations (Maxwell's equations).
  • the three orientation angles are treated as inverted parameters, i.e., the unknowns to be solved for.
  • the invention includes three basic steps, summarized in the flowchart of FIG. 6 : (i) prepare data for inversion (step 61 ); (ii) create an initial model (step 62 ); and (iii) invert data for receiver orientations (step 63 ).
  • EM signals decay exponentially with distance from the source (or, transmitter) for a given frequency.
  • the receiver cannot record high quality signals when the source is far away from the receiver because of ambient noises.
  • the receiver is saturated because of the limited dynamic measurement range. So the measured signals are distorted.
  • data are selected from such intermediate source-receiver offsets such that the source can generate signals strong enough at the receiver location to have good S/N (signal-to-noise ratio), but not too strong to saturate the receiver.
  • accurate source and receiver geometry measurements are required for the selected data.
  • geometric does not include angular orientation of the receivers, of course; as explained, this particular geometric feature cannot be measured with sufficient accuracy.
  • orientations of transmitter for example, azimuth and pitch for HED source
  • coordinates of both the receiver and transmitter for example, azimuth and pitch for HED source
  • data may not be ideal for inversion because of effects such as source instability, individual receiver electronic characteristic, temporally changing natural EM signals, and oceanic waves.
  • the user of the present invention may wish to manually pick data to use, possibly with the help of interactive data display software, or according to experience.
  • both amplitude and phase are typically obtained for each EM field component that is measured.
  • Either amplitude or phase data, or both, can be used for the inversion step of the present invention.
  • the phase data are assessed as having accuracy problem, in which case amplitude alone would be preferred for use in the inversion.
  • both amplitude and phase data of both the electric and magnetic fields, all six components, are included in the inversion.
  • Some vertical component data are important to determine the tilts. Vertical component data are preferably about one third of the total data.
  • At least 3 (independent) data points are needed to uniquely and sufficiently determine the 3 angles of the receiver, where a value of E X (either amplitude or phase) for one receiver/source position would constitute an example of a single data point.
  • E X either amplitude or phase
  • data for as many EM components as possible are preferably included because of noise and the different sensitivity of each component relative to each orientation angle. It is also preferable, but certainly not essential, to include as many frequencies and source-receiver combinations as possible. More data are more expensive to acquire, and require more computer time to process, but give more accurate results.
  • CSEM survey data are measured in the time domain.
  • the present inventive method is preferably performed in the frequency domain, in which embodiments the data must be transformed to the frequency domain by Fourier transformation or other methods.
  • the frequency content of the source waveform may be known, in which case amplitude and phase information for a specific frequency can be extracted from the measured data by data fitting techniques. All such methods shall be referred to herein as transforming the data to the frequency domain.
  • the data become complex numbers.
  • the present inventive method may be performed using only the real part of the selected data, or only the imaginary part, or both. Equivalently, as stated above, the invention may be performed with only amplitude data, or only phase data, or both.
  • An initial model is needed for inversion, which includes 3 receiver orientation angles and resistivity model. Electromagnetic source parameters such as source strength and frequency must also be included in the model as well as any needed (in the inversion step) receiver parameters such as receiver antenna length, and the field source and receiver geometry (the acquisition system must accurately record the geometry). This initial model should be created to be as realistic as possible.
  • the inversion process (discussed below) must of course be performed by numerical methods, beginning with a first guess of the three receiver orientation angles. A good initial guess makes the inversion converge quickly and avoids the pitfall of a local minimum solution for the inversion.
  • Receiver azimuth determined by other methods such as the polarization analysis can be used in the initial model.
  • the seafloor slope is normally not steep, and therefore the angles of two horizontal channel tilts can be set to be zero in the initial model.
  • the resistivity model can be a layered model consisting of air, seawater, and sedimentary seafloor. Seawater resistivity changes with depth and often is measured for each survey area. This measured seawater resistivity column should be used in the initial model if available. Otherwise, the seawater resistivity column can be estimated by empirical formula; see, for example, Chave et al, Electromagnetic Methods in Applied Geophysics , M. Nambighian, Ed., Society of Exploration Geophysicists, Vol. 2, 932 (1991).
  • the sedimentary seafloor can simply be a half-space, or composed of a number of layers, or a more sophisticated model with inputs from other measurements such as seismic survey.
  • the receiver orientation angles are needed in order to more accurately determine the subsurface resistivity structure. Accordingly, it may be difficult to arrive at a good guess for the resistivity model in the inversion for the orientation angles.
  • the prepared data are inverted for both the receiver orientation angles and the earth's resistivity model simultaneously.
  • the inversion is for the receiver orientation angles only, in which instances the results will depend on the accuracy of the assumed resistivity model.
  • the resistivity model is determined using the orientation angles found by one application of the present invention, the inversion for the orientation angles may be repeated, and then the resistivity model inversion can be performed a second time. This cycle may be iterated until desired stop criteria are obtained.
  • the inversion calculations may be performed in 1D, 2D, or 3D.
  • This invention uses inversion to determine all three angles which are necessary to define the receiver orientations, rather than just the receiver azimuth as proposed by Mittet, et al.
  • This data set was then used to test how well the present inventive method could determine the receiver orientations.
  • the inversion process was set up for simultaneously determining the receiver orientations and resistivity model.
  • the initial resistivity model consisted of air, seawater and a uniform half-space for the sedimentary seafloor and the initial angles for receiver were (300.0, 0.0, 0.0).
  • the recovered angles are very close to the angles used to generate the synthetic data, demonstrating the accuracy of the inventive method.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Electromagnetism (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
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  • Geophysics And Detection Of Objects (AREA)
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US70181705P 2005-07-22 2005-07-22
PCT/US2006/025247 WO2007018810A1 (fr) 2005-07-22 2006-06-28 Procede destine a determiner des orientations de recepteur

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EP (1) EP1922660A1 (fr)
CN (1) CN101228529B (fr)
AU (1) AU2006276871B2 (fr)
BR (1) BRPI0613598A2 (fr)
CA (1) CA2616061C (fr)
EA (1) EA011052B1 (fr)
MA (1) MA29740B1 (fr)
MX (1) MX2008000922A (fr)
MY (1) MY141323A (fr)
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GB2441787A (en) * 2006-09-15 2008-03-19 Electromagnetic Geoservices As Method of determining the orientation of an electric and magnetic receiver deployed remotely
GB2442244A (en) * 2006-09-29 2008-04-02 Electromagnetic Geoservices As Determining the position and orientation of electromagnetic receivers
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CN102305948B (zh) * 2011-05-25 2016-05-25 湖南继善高科技有限公司 测量地下电阻率立体变化的三维人工源电磁勘探方法
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WO2015051287A1 (fr) * 2013-10-04 2015-04-09 Schlumberger Canada Limited Procédés et appareils de production d'un modèle de formation
US10436928B2 (en) * 2014-12-19 2019-10-08 International Business Machines Corporation Detection and imaging of subsurface high impedance contrast objects
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CN107290769B (zh) * 2016-04-12 2019-12-24 华北电力大学 核电厂点源体源组合的复合辐射源强逆推方法及系统
CN107290770B (zh) * 2016-04-12 2019-12-24 华北电力大学 核电厂点线面体组合的复合辐射源强逆推方法及系统
CN111880235B (zh) * 2020-08-05 2023-03-28 中国海洋大学 海洋电磁地层各向异性电阻率与发射源姿态联合反演方法
CN111856597B (zh) * 2020-08-05 2023-03-21 中国海洋大学 拖曳式海洋电磁地层电阻率与接收站位置联合反演方法
US12044819B2 (en) * 2021-06-14 2024-07-23 Halliburton Energy Services, Inc. Resistivity determination from one transmitter and one receiver antennas
CN119312472B (zh) * 2024-09-23 2025-05-13 中国科学院微小卫星创新研究院 航天器单机磁源确定方法、电子设备及存储介质

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AU2006276871B2 (en) 2011-02-10
BRPI0613598A2 (pt) 2012-11-06
AU2006276871A1 (en) 2007-02-15
MX2008000922A (es) 2008-03-18
WO2007018810A1 (fr) 2007-02-15
MY141323A (en) 2010-04-16
CA2616061C (fr) 2014-09-16
EP1922660A1 (fr) 2008-05-21
US20090171587A1 (en) 2009-07-02
CA2616061A1 (fr) 2007-02-15
EA200800404A1 (ru) 2008-06-30
EA011052B1 (ru) 2008-12-30
NO20080004L (no) 2008-02-13
CN101228529B (zh) 2010-09-29
MA29740B1 (fr) 2008-09-01
CN101228529A (zh) 2008-07-23

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